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.TH FSCK 8
.UC
.SH NAME
fsck \- file system consistency check and interactive repair
.SH SYNOPSIS
.B fsck
.BR \-p "[ # ]"
[
filesystem ...
]
.br
.B fsck
[
.B \-y
] [
.B \-n
] [
.BR \-s X
] [
.BR \-S X
] [
.B \-t
filename
] [
filesystem 
] ...
.SH DESCRIPTION
The first form of
.I fsck
preens a standard set of file systems or the specified file systems.
It is normally used in the script
.I /etc/rc
during automatic reboot.
In this case
.I fsck
reads the table
.I /etc/fstab
to determine which file systems to check.
It uses the information there to inspect groups of disks in parallel taking
maximum advantage of i/o overlap to check the file systems
as quickly as possible.
Normally, the root file system will be checked on pass 1, other
``root'' (``a'' partition) file systems on pass 2, other
small file systems on separate passes (e.g. the ``d'' file systems
on pass 3 and the ``e'' file systems on pass 4), and finally
the large user file systems on the last pass, e.g. pass 5.
Only one file system from each disk should be checked in each pass.
A pass number of 0 in fstab causes a disk to not be checked; similarly
partitions which are not shown as to be mounted ``rw'' or ``ro''
are not checked.
A number or range of numbers may be given after the
.B \-p
to start or end the check at a specified pass number.
A single number specifies the starting pass (e.g. \-p2 or \-p2\-);
a range specifies the starting and endig passes (\-p2\-4).
A missing start means to start with pass 1 (\-p\-2).
These can be used to stop fsck to mount a temporary file system
before continuing the check on larger file systems requiring scratch files.
.PP
The system normally takes care that only a restricted class of innocuous
inconsistencies can happen unless hardware or software failures intervene.
These are limited to the following:
.IP
Unreferenced inodes
.ns
.IP
Link counts in inodes too large
.ns
.IP
Missing blocks in the free list
.ns
.IP
Blocks in the free list also in files
.ns
.IP
Counts in the superblock wrong
.ns
.IP
Allocated inodes in the free inode list
.PP
These are the only inconsistencies which
.I fsck
with the
.B \-p
option will correct; if it encounters other inconsistencies, it exits
with an abnormal return status and an automatic reboot will then fail.
For each corrected inconsistency one or more lines will be printed
identifying the file system on which the correction will take place,
and the nature of the correction.  After successfully correcting a file
system,
.I fsck
will print the number of files on that file system and the number of
used and free blocks.
.B Warning:
kernel changes are required to limit the types of inconsistencies,
and
.B "fsck \-p"
makes assumptions about the kernel's actions in repairing these.
Vmunix, PDP-11 2.9BSD with the UCB_FSFIX option
and PDP-11 2.10BSD Unix kernels have the
appropriate modifications;
the
.B \-p
option should not be used on other systems.
.PP
Without the
.B \-p
option,
.I fsck
audits and interactively repairs inconsistent conditions for file systems. 
If the file system is inconsistent the operator is prompted for concurrence
before each correction is attempted.
It should be noted that a number of the corrective actions which are not
fixable under the
.B \-p
option will result in some loss
of data.
The amount and severity of data lost may be determined from the diagnostic
output.
The default action for each consistency correction
is to wait for the operator to respond \fByes\fP or \fBno\fP.
If the operator does not have write permission 
.I fsck
will default to a 
.BR "\-n " action.
.PP
.I Fsck
has more consistency checks than
its predecessors
.IR "check, dcheck, fcheck, " "and" " icheck"
combined.
.PP
The following flags are interpreted by
.I fsck.
.TP 6
.B  \-\^y
Assume a yes response to all questions asked by 
.I fsck;
this should be used with great caution as this is a free license
to continue after essentially unlimited trouble has been encountered.
.TP 6
.B  \-\^n
Assume a no response to all questions asked by 
.I fsck;
do not open the file system for writing.
.TP 6
.BR \-\^s \fIX
Ignore the actual free list and (unconditionally) reconstruct a new
one by rewriting the superblock of the file system.  
The file system should be unmounted while this is done; if this
is not possible, care should be taken that the system is quiescent
and that it is rebooted immediately afterwards.
This precaution is necessary so that the old, bad, in-core copy
of the superblock will not continue to be used, or written on the file system.
.IP
The
.BR \-s \fIX
option allows for creating an optimal free list organization.
The following forms of
.I X
are supported for the following devices:
.sp
.nf
	\-s3 (RP03)
	\-s4 (RP04, RP05, RP06)
	\-sBlocks-per-cylinder\fB:\fPBlocks-to-skip (for anything else)
.fi
.IP "" 6
If 
.I X
is not given,
the values used when the file system was created
are used.
If these values were not specified, then the value
.I 400:9
is used.
.TP 6
.BR \-\^S \fIX
Conditionally reconstruct the free list. This option
is like
.BR \-s \fIX
above except that the free list is rebuilt only
if there were no discrepancies discovered in the
file system. Using
.B \-S
will force a no response to all questions asked
by
.I fsck.
This option is useful for forcing free list reorganization
on uncontaminated file systems.
.TP 6
.B \-\^t
If
.I fsck
cannot obtain enough memory to keep its tables,
it uses a scratch file. If the \f3\-t\fP option is
specified, the file named in the next argument
is used as the scratch file, if needed. Without the
.BR "\-t " flag,
.I fsck
will prompt the operator for the name of the
scratch file. The file chosen should not be on the
file system being checked, and if it is not
a special file or did not already exist, it is
removed when
.I fsck
completes.
.PP
If no file systems are given to 
.I fsck
then a default list of file systems is read from
the file
.IR /etc/fstab .
.PP
.ne 10
Inconsistencies checked are as follows:
.TP 6
1.
Blocks claimed by more than one inode or the free list.
.br
.br
.ns
.TP 6
2.
Blocks claimed by an inode or the free list outside the range of the file system.
.br
.br
.ns
.TP 6
3.
Incorrect link counts.
.br
.br
.ns
.TP 6
4.
Size checks:
.br
.ns
.IP "" 12
Directory size not 16-byte aligned.
.br
.br
.ns
.TP 6
5.
Bad inode format.
.br
.br
.ns
.TP 6
6.
Blocks not accounted for anywhere.
.br
.br
.ns
.TP 6
7.
Directory checks:
.br
.br
.ns
.IP "" 12
File pointing to unallocated inode.
.br
Inode number out of range.
.br
.br
.ns
.TP 6
8.
Super Block checks:
.br
.br
.ns
.IP "" 12
More than 65536 inodes.
.br
More blocks for inodes than there are in the file system.
.br
.br
.ns
.TP 6
9.
Bad free block list format.
.br
.br
.ns
.TP 6
10.
Total free block and/or free inode count incorrect.
.br
.ns
.TP 6
11.
Allocated inodes on the free inode list in the superblock.
.PP
Orphaned files and directories (allocated but unreferenced) are,
with the operator's concurrence, reconnected by
placing them in the 
.I lost+found
directory.
The name assigned is the inode number. The only restriction
is that the directory 
.I lost+found
must preexist
in the root of the file system being checked and
must have empty slots in which entries can be made.
This can be accomplished manually by making 
.IR lost+found ,
copying a number of files to the directory, and then removing them
(before
.I
fsck
is executed).
.IR Mkfs (8)
will automatically create a
.I lost+found
directory.
.PP
Checking the raw device is almost always faster.
The root device should not be checked using the raw device,
however, since it cannot be unmounted.
.SH FILES
.ta 2i
/etc/fstab	default list of file systems to check
.SH DIAGNOSTICS
The diagnostics produced by 
.I fsck
are intended to be self-explanatory.
The exit codes with the
.B \-p
option are 0 (no problems that weren't fixed), 4 (root file system was
modified), 8 (problems that couldn't be fixed) and 12
.RI ( fsck
was interrupted).
.SH "SEE ALSO"
filsys(5), fstab(5), crash(8), mkfs(8), mklost+found(8), reboot(8)
.br
T. J. Kowalski,
.I "FSCK \- The UNIX File System Check Program"
.SH BUGS
Inode numbers for
.BR . ""
and
.BR .. ""
in each directory should be checked for validity.
